1. Field of the Invention
The present invention relates to a mechanical sliding sleeve for use in downhole, oilfield operations.
2. Description of Related Art
In downhole oilfield operations, it is often desirable to selectively allow fluid communication between an interior of a tubing string and an annulus defined by the tubing string and a well casing. A “sliding sleeve,” which typically is made up as an integral part of a tubing string, provides such functionality. The sliding sleeve utilizes a sliding isolation sleeve to isolate fluid communication between the annulus and the interior of the tubing string. When in a “closed” configuration, the isolation sleeve is slidingly positioned to inhibit flow between the interior of the tubing string and the annulus. When in an “open” configuration, the isolation sleeve is slidingly positioned to allow flow between the interior of the tubing string and the annulus.
Such isolation sleeves are typically operated either by mechanical means or by hydraulic means. Mechanically-operated isolation sleeves are operated by running a “shifting tool” into a bore of the sliding sleeve and using the tool to physically move the isolation sleeve between the open and closed positions. Moving parts of conventional mechanically-operated isolation sleeves, however, are exposed to downhole fluids that contain debris, which can foul the moving parts. Such debris and other deposits from downhole fluids can readily form obstructions about the moving parts of sliding sleeves, sometimes encasing the sleeve in a shell, thus preventing the shifting tool from shifting the sleeve. In thermal wells, the rate and quantity at which deposits form on the sliding sleeve is greatly accelerated, as compared to non-thermal wells. Normally, extensive cleaning of such shifting sleeves is required before the sleeve can be operated. However, cleaning does not always ensure proper operation of such sleeves. Moreover, the position of a conventional mechanically-operated sliding sleeve in a tubing string is often difficult to locate when the shifting tool is lowered into the tubing string.
Hydraulically-operated isolation sleeves utilize hydraulic circuits incorporated into the sliding sleeve that route hydraulic fluid to move the isolation sleeve between the open and closed positions. Such hydraulically-operated isolation sleeves are more complex, are susceptible to hydraulic fluid leaks, and have larger annular profiles than mechanically-operated isolation sleeves. Moreover, hydraulically-operated sliding sleeves are more difficult and time consuming to install. Furthermore, a secondary method of shifting hydraulically-operated sliding sleeves is desirable in case the hydraulic system used to primarily operate the sliding sleeve fails. In some cases, providing fluid communication between the tubing string and the annulus may entail machining an opening through the sliding sleeve by, for example, milling.
There are many designs of sliding sleeves well known in the art, however, considerable shortcomings remain.